1. Field of the Invention
The present invention relates to improvements in sickle or knife assembly constructions for argricultural hay and harvesting machinery.
2. Description of the Prior Art
Sickle knife assemblies have been used for cutting hay and standing grain for many years, and generally comprise an elongated knifeback bar that is equal in length to the desired length of the knife assembly to be used, and then a plurality of individual sickle knife sections are usually riveted or bolted to the knifeback bar. The knife assembly is driven at one end with a knife head, and is suitably supported on a sickle bar and reciprocated back and forth for cutting. The loads between the knife sections and the knifeback create shear in the rivets or bolts, and of course the longer the knife assembly, the greater the shear loads that are incurred at the knife head end of the knife assembly. Knife assembly lengths extend into the range of 30 feet or more, and shipment and storage of them becomes a problem. Further, damage to a portion of the knife assembly requires individually replacing the knife sections, which is time consuming.
In the past, there have been sickle knife assemblies that have been made up into a plurality of individual short sections that are joined together to make the elongated assembly. For example, U.S. Pat. No. 1,340,868 shows a knife assembly where short individual portions of lengths of the knifeback are riveted together, with each knifeback portion supporting a single knife sections. The junctions between the individual knifeback portions are made so that they interfit in a type of V-notch in one portion and a mating arrowhead end in the mating portion. The V-notches form undercuts that are stress raisers, and with the very short individual portions the rigidity of the knife assembly is reduced substantially.
U.S. Pat. No. 329,696 shows a knife assembly that has short knifeback lengths or portions that have ridged or toothed ends that overlap and then through rivets are used to hold the knifeback portions together. The knifeback portions have a length equal to the width of one knife section. The short knifeback portions are relatively expensive to manufacture, will not easily stay straight during assembly or use, and the individual knifeback portions will tends to rotate slightly relative to each other in the rivet holes so that strength is reduced substantially. The interlocking teeth shown in U.S. Pat. No. 329,696 are difficult to manufacture sufficiently accurately to avoid relative movement between the adjacent knifeback portions in longitudinal direction as the knife assembly is reciprocated. Once there is any movement at all, the knife assembly will hammer itself apart very quickly.
U.S. Pat. No. 1,233,950 also shows a sickle bar or knife assembly made with a plurality of very short long knifeback portions held end-to-end and with backing plates on the side of the knifeback opposite from the knife sections. The knifeback thus has an extra thickness of material on the back side, which requires using flush rivets, that are difficult to get tight, or specialized guards to support the knifeback. This type of device has three rivet shear lines to carry the load, but to be reliable the clamping force and friction between the mating parts at the splice of the knifeback have to be great enough to carry the lengthwise loads and thus with a number of short knifeback portions, particularly ones that form splices adjacent the drive head for the knife assembly, cause problems and early failure.